Critics contended the math in a tweet sent by Donald Trump's son comparing Syrians to Skittles doesn't add up.

On 19 September 2016, Donald Trump, Jr., son of the current Republican presidential nominee, ppsyed a controversial tweet likening the “Syrian refugee problem” to a bowl of poisoned Skittles, suggesting that a poisonous few made the whole batch dangerously unpalatable:

Trump, Jr.’s tweet appeared against the backdrop of the arrest of Ahmad Khan Rahami (a naturalized U.S. citizen who was born in Afghanistan) in connection with bombs discovered and detonated in New Jersey and Manhattan on 17 September 2016. The tweet quickly went viral and was shared tens of thousands of times, but the analogy of Skittles related to the Syrian refugee crisis was not original to Trump.

For example, comedian John Oliver criticized politician Mike Huckabee’s use of a similar comparison in late 2015:

An October 2015 report from the Migration Policy Institute examined the numbers:

As Congress and others react to the Obama administration’s announcement that the refugee resettlement program will increase from the current 70,000 level to 85,000 next year and 100,000 in 2017, some are objecting on national security grounds.

The reality is this: The United States has resettled 784,000 refugees since September 11, 2001. In those 14 years, exactly three resettled refugees have been arrested for planning terrorist activities — and it is worth noting two were not planning an attack in the United States and the plans of the third were barely credible.

The Washington Post similarly looked at the analogy through numbers derived by the Cato Institute:

So let’s figure out what the analogy is. The libertarian (and Koch brothers-backed) think tank Cato Institute published a report last week assessing the risk posed by refugees. That report stated that, each year, the risk to an American of being killed by a refugee in a terror attack is 1 in 3.64 billion, as Huffington Post’s Elise Foley noted on Twitter. From the report:

From 1975 through 2015, the annual chance that an American would be murdered in a terrorist attack carried out by a foreign-born terrorist was 1 in 3,609,709. Foreigners on the Visa Waiver Program (VWP) killed zero Americans in terrorist attacks, whereas those on other tourist visas killed 1 in 3.9 million a year. The chance that an American would be killed in a terrorist attack committed by a refugee was 1 in 3.64 billion a year.

In other words, for every 10.92 billion years that Americans live — one Skittle, if you will — refugees will kill an American in a terror attack in three … we’re talking about one-and-a-half Olympic swimming pools of Skittles. Wrigley produces 200 million Skittles a day, so this is the entire production line for more than 54 days, transported to an oversized swimming pool and dumped in to the top. And in that pool: Three poison Skittles.

Wrigley, the makers of Skittles, issued a terse statement about rejecting the analogy as inappropriate:

Skittles are candy. Refugees are people. We don’t feel it’s an appropriate analogy. We will respectfully refrain from further commentary as anything we say could be misinterpreted as marketing.

The “some are poisonous, so we can’t take that chance” analogy appeared in another form decades before, in a children’s book called The Poisonous Mushroom (or, in its original German, Der Giftpilz):

A mother and her young boy are gathering mushrooms in the German forest. The boy finds some poisonous ones. The mother explains that there are good mushrooms and poisonous ones, and, as they go home, says:

“Look, Franz, human beings in this world are like the mushrooms in the forest. There are good mushrooms and there are good people. There are poisonous, bad mushrooms and there are bad people. And we have to be on our guard against bad people just as we have to be on guard against poisonous mushrooms. Do you understand that?”

“Yes, mother,” Franz replies. “I understand that in dealing with bad people trouble may arise, just as when one eats a poisonous mushroom. One may even die!”

“And do you know, too, who these bad men are, these poisonous mushrooms of mankind?” the mother continued.

Franz slaps his chest in pride:

“Of course I know, mother! They are the Jews! Our teacher has often told us about them.”

The mother praises her boy for his intelligence, and goes on to explain the different kinds of “poisonous” Jews: the Jewish pedlar, the Jewish cattle-dealer, the Kosher butcher, the Jewish doctor, the baptised Jew, and so on.

“However they disguise themselves, or however friendly they try to be, affirming a thousand times their good intentions to us, one must not believe them. Jews they are and Jews they remain. For our Volk they are poison.”

“Like the poisonous mushroom!” says Franz.

The writer of that children’s book, Julius Streicher, was also an early follower of Adolf Hitler and the publisher of Der Stürmer, a German weekly newspaper specializing in Nazi propaganda. He was sentenced to death and hanged in 1946.